PAGE
	SBTTL "--- MAIN LOOP ---"

MLOOP:	JSR	ROMOUT		; FOR SAFETY
	DEC	RAND2		; RANDOMNESS
	DEC 	RAND2

	CLR 	ARGCNT		; RESET # ARGUMENTS
	JSR	NEXTPC		; GET NEXT Z-BYTE
	STA	OPCODE		; SAVE OPCODE

	IF	DEBUG
	LDB	#'0'
	JSR	DOBUG
	LDA	OPCODE
	ENDIF

	LBPL	OP2		; 2-OP IF POSITIVE
	CMPA	#176
	BLO	OP1		; IT'S A 1-OP
	CMPA	#192
	BLO	OP0		; IF NOT A 0-OP ...

	; HANDLE AN X-OP

OPEXT:	JSR	NEXTPC		; GET ARGUMENT BYTE
	STA	TEMP2		; HOLD IT HERE
	CLR	TEMP2+1		; INIT LOOP INDEX
	BRA	OPX1

OPX0:	LDA 	TEMP2		; GRAB ARG BYTE
	ASLA			; SHIFT TO BITS 7 & 6
	ASLA
	STA	TEMP2		; SAVE RESULT

OPX1:	ANDA	#%11000000	; MASK OUT GARBAGE
	BNE	OPX2
	JSR	GETLNG		; 00 = LONG IMMEDIATE
	BRA	OPXNXT

OPX2:	CMPA	#%01000000
	BNE	OPX3
	JSR	GETSHT		; 01 = SHORT IMMEDIATE
	BRA	OPXNXT

OPX3:	CMPA	#%10000000
	BNE	OPX4		; 11 = NO MORE VARIABLES
	JSR	GETVAR		; 10 = VARIABLE

OPXNXT:	LDB	TEMP2+1		; GET INDEX
	LDX	#ARG1		; BASE ADDR OF ARGS
	ABX			; ADD OFFSET IN B
	LDD	TEMP		; GRAB THE ARGUMENT'S VALUE
	STD	,X		; AND SAVE IT
	INC 	ARGCNT		; KEEP TRACK
	INC	TEMP2+1		; UPDATE
	INC	TEMP2+1		; ARGUMENT INDEX
	LDA	TEMP2+1		; DONE 4 ARGS YET?
	CMPA	#8
	BLO	OPX0		; NO, KEEP GRABBING

	; DISPATCH THE X-OP

OPX4:	LDB	OPCODE		; RETRIEVE THE OPCODE
	CMPB	#224		; IS IT AN EXTENDED 2-OP?
	LBLO	OP2EX		; YES, HANDLE LIKE A 2-OP
	ANDB	#%00011111	; ELSE ISOLATE OP BITS
	CMPB	#NOPSX		; COMPARE TO LEGAL # OF X-OPS
	BLO	DISPX		; CONTINUE IF OKAY

	; *** ERROR #1 -- ILLEGAL X-OP ***

	LDA	#1
	JSR	ZERROR

DISPX:	LDX	#OPTX		; X-OP DISPATCH TABLE
DODIS:	ASLB			; FORM A WORD-OFFSET INTO IT
	ABX			; ADD THE OFFSET

	IF	DEBUG
	PSHS	X
	LDB	#'1'
	JSR	DOBUG
	PULS	X
	ENDIF

	JSR	[,X]		; HANDLE THE OPCODE
	JMP	MLOOP		; AND GO BACK FOR ANOTHER

	; HANDLE A 0-OP

OP0:	LDX	#OPT0		; 0-OP DISPATCH TABLE
	LDB	OPCODE		; FETCH OPCODE
	ANDB	#%00001111	; ISOLATE OP BITS
	CMPB	#NOPS0		; OPCODE OUT OF RANGE?
	BLO	DODIS		; NO, GO DISPATCH IT

	; *** ERROR #2 -- ILLEGAL 0-OP ***

	LDA	#2
	JSR	ZERROR

	; HANDLE A 1-OP

OP1:	ANDA	#%00110000	; ISOLATE ARG BITS
	BNE	OP1A
	JSR	GETLNG		; 00 = LONG IMMEDIATE
	BRA	OP1EX

OP1A:	CMPA	#%00010000
	BNE	OP1B
	JSR	GETSHT		; 01 = SHORT IMMEDIATE
	BRA	OP1EX

OP1B:	CMPA	#%00100000
	BEQ	OP1C

	; *** ERROR #3 -- ILLEGAL 1-OP ***

BADOP1:	LDA	#3
	JSR	ZERROR

OP1C:	JSR	GETVAR		; 10 = VARIABLE

OP1EX:	LDD	TEMP
	STD	ARG1		; GRAB THE ARGUMENT
	INC	ARGCNT		; ONE ARGUMENT
	LDX	#OPT1		; ADDR OF 1-OP DISPATCH TABLE
	LDB	OPCODE		; RESTORE OPCODE
	ANDB	#%00001111	; ISOLATE OP BITS
	CMPB	#NOPS1		; IF OPCODE OUT OF RANGE,
	BHS	BADOP1		; REPORT IT
	BRA	DODIS		; ELSE DISPATCH THE 1-OP

	; HANDLE A 2-OP

OP2:	ANDA	#%01000000	; ISOLATE 1ST ARG BIT
	BNE	OP2A
	JSR	GETSHT		; 0 = SHORT IMMEDIATE
	BRA	OP2B

OP2A:	JSR	GETVAR		; 1 = VARIABLE

OP2B:	LDD	TEMP		; GRAB VALUE
	STD	ARG1		; SAVE IN ARG1
	INC	ARGCNT

	LDA	OPCODE		; RESTORE OPCODE
	ANDA	#%00100000	; ISOLATE 2ND ARG BIT
	BNE	OP2C
	JSR	GETSHT		; 0 = SHORT IMMEDIATE
	BRA	OP2D

OP2C:	JSR	GETVAR		; 1 = VARIABLE

OP2D:	LDD	TEMP		; GRAB 2ND VALUE
	STD	ARG2		; STORE AS ARG2
	INC	ARGCNT

OP2EX:	LDX	#OPT2		; ADDR OF 2-OP DISPATCH TABLE
	LDB	OPCODE		; RESTORE YET AGAIN
	ANDB	#%00011111	; ISOLATE OP BITS
	CMPB	#NOPS2		; OPCODE IN RANGE?
	LBLO	DODIS		; YES, GO DISPATCH IT

	; *** ERROR #4 -- ILLEGAL 2-OP ***

BADOP2:	LDA	#4
	JSR	ZERROR

	END